As the air-fuel ratio sensor, there is a two-cell type having an electromotive force cell and an oxygen pump cell which are oxygen concentration cells. In the air-fuel ratio sensor of the two-cell type, a pump current flowing in an oxygen pump cell is controlled so that an output voltage of the electromotive force cell reaches a target value, and the pump current is detected as a sensor current corresponding to an air-fuel ratio (for example, refer to Patent Document 1).
Also, as the air-fuel ratio sensor, there is a one-cell type having a single cell into which a current corresponding to the air-fuel ratio flows in a state where a voltage is applied thereto. In the air-fuel ratio sensor of the one-cell type, the current flowing in the cell is detected as the sensor current corresponding to the air-fuel ratio (for example, refer to Patent Document 2).
In each of the air-fuel ratio sensor of the one-cell type and the air-fuel ratio sensor of the two-cell type, to manufacture a control device having a dedicated hardware is disadvantageous to a reduction in the manufacturing cost of the control device since the variety of the control devices increases, and the number of manufacturing the respective control devices does not increase.
[Patent Document 1] JP-A-10-48180 (corresponding to U.S. Pat. No. 6,120,677)
[Patent Document 2] JP-A-11-230931